Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “microbial competition”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 307 records · Page 17Linked to original sources
PubMed2005

The role of innate immune responses in the outcome of interspecies competition for colonization of mucosal surfaces.

Since mucosal surfaces may be simultaneously colonized by multiple species, the success of an organism may be determined by its ability to compete with co-inhabitants of its niche. To explore the contribution of host factors to polymicrobial competition, a murine model was used to study the initiation of colonization by Haemophilus influenzae and Streptococcus pneumoniae. Both bacterial species, which occupy a similar microenvironment within the nasopharynx, persisted during colonization when given individually. Co-colonization, however, resulted in rapid clearance of S. pneumoniae from the upper respiratory tract, associated with increased recruitment of neutrophils into paranasal spaces. Systemic depletion of either neutrophil-like cells or complement was sufficient to eliminate this competitive effect, indicating that clearance was likely due to enhanced opsonophagocytic killing. The hypothesis that modulation of opsonophagocytic activity was responsible for host-mediated competition was tested using in vitro killing assays with elicited neutrophil-like cells. Components of H. influenzae (but not S. pneumoniae) stimulated complement-dependent phagocytic killing of S. pneumoniae. Thus, the recruitment and activation of neutrophils through selective microbial pattern recognition may underlie the H. influenzae-induced clearance of S. pneumoniae. This study demonstrates how innate immune responses may mediate competitive interactions between species and dictate the composition of the colonizing flora.

Journal Article↗
PubMed2001

Mononuclear cells ingest E. coli opsonized by investigational intravenous immunoglobulin preparations in the absence of complement more efficiently than polymorphonuclear phagocytes.

OBJECTIVE: The increasing use of intravenous immunoglobulins (IVIg) to treat systemic inflammatory, mostly autoimmune, diseases raises the concern that their competition for FcgammaReceptor (FcgammaR) binding with immune complexes might interfere with the removal of opsonized microbial agents more than it favoured their opsonophagocytosis. METHODS: Using a sensitive FACS-based phagocytosis assay allowing for the identification of the phagocytosing cell-type, we have tested the relative capacity of Pentaglobin and two investigational IVIg preparations, IVIgG and IVIgM, to promote E. coli phagocytosis. The plasma IL-8 levels 4 h after phagocytosis were measured by ELISA. RESULTS: Heat inactivated, complement (C) depleted serum allowed about 25% polymorphonuclear leukocytes (PMNLs) and 15% monocytes (MNs) of 16 donors to phagocyte E. coli. The addition of IVIg favoured mean phagocytosis by MNs to 55%, but by PMNLs only to 25%. The addition of fresh autologous plasma as a C source resulted in a boost of phagocytosing capacity to reach >90% of the PMNLs and >72% of the MNs. Blockade of FcgammaRII and FcgammaRI using monoclonal antibodies (mAb) reduced phagocytosis and IL-8 release. CONCLUSION: We conclude that excess IVIgG/M preparations added to a phagocytic system of PMNLs and MNs, without preopsonization of E. coli, promotes phagocytosis as expected, but MNs rather than PMNLs do this more thoroughly on their own.

Escherichia coli↗
PubMed1995

Functional interaction of ligands and receptors of the hematopoietic superfamily in yeast.

Circulating peptide hormones and growth factors interact with cell surface receptors to initiate specific cellular responses. These complexes can consist of a simple association between two proteins or a more elaborate association of multiple proteins. We describe the functional expression of ligands and corresponding receptors in a microbial system useful for the rapid dissection of these important protein interactions. GH or PRL and extracellular domains of their respective receptors were functionally expressed as fusion proteins in an extended two-hybrid protein-protein interaction system. Reversible and specific ligand-receptor interactions were demonstrated by concurrent expression of free ligand peptides (GH or PRL) as binding competitors. The versatility established by expressing three heterologous proteins allowed for the investigation of higher order structures. Ligand-dependent GH receptor dimerization was demonstrated but PRL receptor dimerization was not observed in an analogous assay, suggesting that these related growth factors may not engage receptors in a similar manner. Additionally, significant association of GH receptors was observed in the absence of ligand, suggesting that there may be substantial avidity between these receptor proteins before ligand binding. Ligand-dependent and ligand-independent receptor dimerization was demonstrated by vascular endothelial growth factor and receptor proteins in similar assays. These findings indicate that extracellular protein interactions such as ligand-receptor association, as well as the formation of higher order protein structures important for the activation of hematopoietic receptors, can be rapidly investigated in this microbial expression system.

Binding, Competitive↗
PubMed2005

Establishment of DsRed.T3_S4T as an improved autofluorescent marker for microbial ecology applications.

Autofluorescent proteins (AFPs), such as green fluorescent protein (GFP) and DsRed, are valuable tools for studying plant-microbe interactions. Nevertheless, because of some limitations, efforts are ongoing to generate improved AFP variants. Several groups have generated variants of GFP with altered spectral characteristics, and faster maturing and brighter variants of DsRed. In this study we used plasmid and chromosomal constructs to test the efficacy of a new variant of DsRed, DsRed.T3_S4T, in Pseudomonas fluorescens F113rif. In addition, we compared the ecological fitness of strains carrying chromosomal copies of EGFP, DsRed or DsRed.T3_S4T. Strains expressing DsRed.T3_S4T fluoresced significantly brighter than strains expressing DsRed. Furthermore, it was found that although all strains grew equally well in vitro, only strains carrying DsRed.T3_S4T functioned as well as wild type in a competitive rhizosphere colonization assay. In particular, it was observed that DsRed.T3_S4T is an improved marker over DsRed for microbial ecology studies in this strain.

Cloning, Molecular↗
PubMed2001

Microbial interactions and biocontrol in the rhizosphere.

The loss of organic material from the roots provides the energy for the development of active microbial populations in the rhizosphere around the root. Generally, saproptrophs or biotrophs such as mycorrhizal fungi grow in the rhizosphere in response to this carbon loss, but plant pathogens may also develop and infect a susceptible host, resulting in disease. This review examines the microbial interactions that can take place in the rhizosphere and that are involved in biological disease control. The interactions of bacteria used as biocontrol agents of bacterial and fungal plant pathogens, and fungi used as biocontrol agents of protozoan, bacterial and fungal plant pathogens are considered. Whenever possible, modes of action involved in each type of interaction are assessed with particular emphasis on antibiosis, competition, parasitism, and induced resistance. The significance of plant growth promotion and rhizosphere competence in biocontrol is also considered. Multiple microbial interactions involving bacteria and fungi in the rhizosphere are shown to provide enhanced biocontrol in many cases in comparison with biocontrol agents used singly. The extreme complexity of interactions that can occur in the rhizosphere is highlighted and some potential areas for future research in this area are discussed briefly.

Bacteria↗
PubMed1994

Adherence of Legionella pneumophila to U-937 cells, guinea-pig alveolar macrophages, and MRC-5 cells by a novel, complement-independent binding mechanism.

In the absence of serum, Legionella pneumophila demonstrated wash-resistant adherence to U-937 cells, primary guinea-pig alveolar macrophages, and MRC-5 cells. Neither complement nor antibody was required for binding. The dynamics of adherence following inoculation of L. pneumophila at increasing 10-fold multiplicities of infection to each of the three host cell types resulted in a first-order kinetic relationship of binding, indicative of one bacterial adhesin molecule recognized by one host cell receptor moiety. Host cell receptor saturation studies showed that depending on the cell type, 2-8% of the bacterial inoculum adhered to cells under these nonopsonic conditions. Preliminary adhesin and receptor characterization studies were performed to define the chemical composition of the binding structures on both the organism and the three different host cell surfaces. The adherence phenomenon was investigated using competitive binding assays in the presence of putative adhesin analogs as well as following treatments modifying the microbial and host cell surface membranes. Attachment was evaluated both by viable bacterial cell colony counts and by indirect immunofluorescent assay. With the exception of aldehyde treatments, the various membrane-modifying regimes and the presence of the adhesin analogs were shown to have no effect on organism or host cell viability. Data suggested that the L. pneumophila adhesin responsible for opsonin-independent binding to these host cells was a protein structure with lectin-like properties. Furthermore, this protein would appear to be intimately associated with carbohydrate or lipid structures located on the bacterial outer membrane.(ABSTRACT TRUNCATED AT 250 WORDS)

Adhesins, Bacterial↗
PubMed2003

Elicitation of plants and microbial cell systems.

Plants show physiological and morphological responses to a range of physical and chemical factors known as 'elicitors'. These responses have been considered as defence reactions 'elicited' by the plants' biochemical factory to ensure their survival, persistence and competitiveness. Recently examples have been cited of elicitation in some fungal and bacterial cultures. Through a chronological survey, this Review considers examples of elicitors and elicitation and describes suggested mechanisms of elicitation in plants and microbial cell cultures. The majority of research in this field has been carried out on the plant systems using complex (undefined) biotic elicitors. Carbohydrates are the main class of compounds used as defined elicitors. This Review focuses on carbohydrates as compounds initiating a defence response in cell cultures. Physiological changes brought about on the plant and microbial cultures include expression of novel metabolites and overproduction of already known products. Recent reports confirming elicitation in microbial cultures are of potential importance, as the relative ease of fermentation and scale-up could open an opportunity for the introduction of useful novel metabolites as well as enhancement of commercially useful bioproducts. In this context, a sound knowledge of the elicitor molecules' structure-function relationships and mechanisms of elicitation is essential.

Bacteria↗
PubMed2001

Influence of the natural microbial flora on the acid tolerance response of Listeria monocytogenes in a model system of fresh meat decontamination fluids.

Depending on its composition and metabolic activity, the natural flora that may be established in a meat plant environment can affect the survival, growth, and acid tolerance response (ATR) of bacterial pathogens present in the same niche. To investigate this hypothesis, changes in populations and ATR of inoculated (10(5) CFU/ml) Listeria monocytogenes were evaluated at 35 degrees C in water (10 or 85 degrees C) or acidic (2% lactic or acetic acid) washings of beef with or without prior filter sterilization. The model experiments were performed at 35 degrees C rather than lower (</=15 degrees C) temperatures to maximize the response of inoculated L. monocytogenes in the washings with or without competitive flora. Acid solution washings were free (<1.0 log CFU/ml) of natural flora before inoculation (day 0), and no microbial growth occurred during storage (35 degrees C, 8 days). Inoculated L. monocytogenes died off (negative enrichment) in acid washings within 24 h. In nonacid (water) washings, the pathogen increased (approximately 1.0 to 2.0 log CFU/ml), irrespective of natural flora, which, when present, predominated (>8.0 log CFU/ml) by day 1. The pH of inoculated water washings decreased or increased depending on absence or presence of natural flora, respectively. These microbial and pH changes modulated the ATR of L. monocytogenes at 35 degrees C. In filter-sterilized water washings, inoculated L. monocytogenes increased its ATR by at least 1.0 log CFU/ml from days 1 to 8, while in unfiltered water washings the pathogen was acid tolerant at day 1 (0.3 to 1.4 log CFU/ml reduction) and became acid sensitive (3.0 to >5.0 log CFU/ml reduction) at day 8. These results suggest that the predominant gram-negative flora of an aerobic fresh meat plant environment may sensitize bacterial pathogens to acid.

Acetic Acid↗
PubMed2004

Are viruses driving microbial diversification and diversity?

Viruses can influence the genetic diversity of prokaryotes in various ways. They can affect the community composition of prokaryotes by 'killing the winner' and keeping in check competitive dominants. This may sustain species richness and the amount of information encoded in genomes. Viruses can also transfer (viral and host) genes between species. Such mechanisms have probably influenced the speciation of prokaryotes. Whole-genome sequencing has clearly revealed the importance of (virus-mediated) gene transfer. However, its significance for the ecological performance of aquatic microbial communities is only poorly studied, although the few available reports indicate a large potential. Here, we present data supporting the hypothesis that viral genes and viral activity generate genetic variability of prokaryotes and are a driving force for ecological functioning and evolutionary change.

Bacteria↗
PubMed2007

Identification of bacterial DNA markers for the detection of human fecal pollution in water.

We used genome fragment enrichment and bioinformatics to identify several microbial DNA sequences with high potential for use as markers in PCR assays for detection of human fecal contamination in water. Following competitive solution-phase hybridization of total DNA from human and pig fecal samples, 351 plasmid clones were sequenced and were determined to define 289 different genomic DNA regions. These putative human-specific fecal bacterial DNA sequences were then analyzed by dot blot hybridization, which confirmed that 98% were present in the source human fecal microbial community and absent from the original pig fecal DNA extract. Comparative sequence analyses of these sequences suggested that a large number (43.5%) were predicted to encode bacterial secreted or surface-associated proteins. Deoxyoligonucleotide primers capable of annealing to a subset of 26 of the candidate sequences predicted to encode factors involved in interactions with host cells were then used in the PCR and did not amplify markers in DNA from any additional pig fecal specimens. These 26 PCR assays exhibited a range of specificity in tests with 11 other animal sources, with more than half amplifying markers only in specimens from dogs or cats. Four assays were more specific, detecting markers only in specimens from humans, including those from 18 different human populations examined. We then demonstrated the potential utility of these assays by using them to detect human fecal contamination in several impacted watersheds.

Animals↗
PubMed1995

Structural studies on human rhinovirus 14 drug-resistant compensation mutants.

Structures have been determined of three human rhinovirus 14 (HRV14) compensation mutants that have resistance to the antiviral capsid binding compounds WIN 52035 and WIN 52084. In addition, the structure of HRV14 is reported, with a site-directed mutation at residue 1219 in VP1. A spontaneous mutation occurs at the same site in one of the compensation mutants. Some of the mutations are on the viral surface in the canyon and some lie within the hydrophobic binding pocket in VP1 below the ICAM footprint. Those mutant virus strains with mutations on the surface bind better to cells than does wild-type virus. The antiviral compounds bind to the mutant viruses in a manner similar to their binding to wild-type virus. The receptor and WIN compound binding sites overlap, causing competition between receptor attachment and antiviral compound binding. The compensation mutants probably function by shifting the equilibrium in favor of receptor binding. The mutations in the canyon increase the affinity of the virus for the receptor, while the mutations in the pocket probably decrease the affinity of the WIN compounds for the virus by reducing favorable hydrophobic contacts and constricting the pore through which the antiviral compounds are thought to enter the pocket. This is in contrast to the resistant exclusion mutants that block compounds from binding by increasing the bulk of residues within the hydrophobic pocket in VP1.

Antiviral Agents↗
PubMed2004

Monitoring the impact of bioaugmentation on the start up of biological phosphorus removal in a laboratory scale activated sludge ecosystem.

The acclimatisation of activated sludge to enhanced biological phosphorus removal (EBPR) conditions requires a period of about 40-100 days but its output remains hazardous. The impact of bioaugmentation on the start-up of a laboratory scale EBPR sequencing batch reactor was evaluated by process parameters measurement and microbial community dynamics monitoring using 16S rDNA targeted polymerase chain reaction-single strand conformation polymorphism electrophoresis (PCR-SSCP). Bioaugmentation: (1) speeded up the installation of good and stable EBPR in the bioaugmented reactor by about 15 days; (2) correlated with the transient enrichment of the sludge in the added microbial populations; and (3) favoured the long-term enrichment of the sludge in the phosphorus-accumulating organism (PAO) Candidatus Accumulibacter phosphatis. However, despite a lag time period, the control non-bioaugmented reactor ended up with comparable reactor parameters and microbial community evolution, suggesting that the same PAO populations were already present from the beginning in the original non-P-accumulating seed sludge. The potential of a true installation of the added microbial populations within the bioaugmented reactor compared to their substitution by indigenous similar populations is discussed. Competition between PAOs and the antagonistic glycogen accumulating organism Candidatus Competibacter phosphatis is also highlighted during EBPR start-up.

Biodegradation, Environmental↗
PubMed2005

Effect of the microbial feed additive Saccharomyces cerevisiae CNCM I-1077 on protein and peptide degrading activities of rumen bacteria grown in vitro.

We investigated the potential of the ruminant feed additive Saccharomyces cerevisiae CNCM I-1077 on protein and peptide degrading activities of the rumen bacterial species Prevotella albensis M384, Streptococcus bovis 20480, and Butyrivibrio fibrisolvens 3071 grown in vitro. Alive or heat-killed yeast cells were added to bacterial cultures in a complex casein-glucose medium. After incubation of the cultures at 39 degrees C under O(2)-free CO(2), peptidase activities were determined in the absence or in the presence of yeasts. Protease activities were detected after PAGE in gelatin-copolymerized gels. In co-incubations of bacteria and live S. cerevisiae I-1077, proteinase activities were reduced compared to the activities in the bacterial monocultures. Measurement of peptidase activities and microbial enumerations in the co-incubations suggested that live yeasts and bacteria interacted in a competitive way, leading to a decrease in peptidase activities. The mechanism responsible for such an effect could be mainly a competition for substrate utilization, but the release of small competitive peptides by the yeast cells is also likely to be implicated.

Animal Feed↗
PubMed2001

In vitro adherence properties of Lactobacillus rhamnosus DR20 and Bifidobacterium lactis DR10 strains and their antagonistic activity against an enterotoxigenic Escherichia coli.

Adhesion and colonisation properties of three probiotic strains namely, Lactobacillus rhamnosus DR20, L. acidophilus HN017, and Bifidobacterium lactis DR10, were determined in vitro using the differentiated human intestinal cell-lines including HT-29, Caco-2, and HT29-MTX, and compared with properties of L. acidophilus LA-1 and L. rhamnosus GG (two commercial probiotic strains). Two independent methods were employed to quantitate the "adhesiveness" of each strain. In the first method, the bacteria adhered to human cells were detected by Gram staining and counted in different fields under a microscope. Bacteria were also radio-labelled and extent of adhesion determined by scintillation counting. All three strains showed strong adhesion with the human intestinal cell lines in vitro. Adhesion indices of the three strains to two cell lines, i.e. HT-29, and Caco-2 varied between 99 +/- 17 and 219 +/- 36. With mucus-secreting cell-line HT29-MTX, the adhesion indices of all the strains were 2-3 times higher. The adhesion indices of L. acidophilus LA-1 and L. rhamnosus GG were comparable to the other three probiotic strains. We also investigated the inhibitory effect of adhering strains against the intestinal cell monolayer colonization by a known enterotoxigenic strain of Escherichia coli (strain O157:H7). Pre-treatment of E. coli O157:H7 with 2.5-fold concentrated cell-free culture supernatants from L. acidophilus HN017, L. rhamnosus DR20 and B. lactis DR10 reduced the culturable E. coli numbers on TSB plates and also reduced the invasiveness and cell association characteristics of this toxic strain. The inhibitory molecules secreted into the spent media by these strains were partially affected by treatments with lactate dehydrogenase, trypsin and proteinase K suggesting that overall inhibition may be due to a synergistic action of lactic acid and proteinaceous substances.

Bacterial Adhesion↗
PubMed1988

Ketone-substrate analogues of Clostridium histolyticum collagenases: tight-binding transition-state analogue inhibitors.

A series of ketone-substrate analogues has been synthesized for the two classes of collagenases from Clostridium histolyticum and shown to be competitive inhibitors. These compounds have sequences that match those of specific peptide substrates for these enzymes. The best inhibitor is the ketone analogue of cinnamoyl-Leu-Gly-Pro-Pro, which has a KI value of 18 nM for epsilon-collagenase, a class II enzyme. This is the tightest binding inhibitor reported for any collagenase to date. Plots of log KI for the inhibitors vs log KM/kcat for the matched substrates for both collagenases are linear with slopes near unity, indicating that the ketones are transition-state analogues. This strongly implies that the ketone carbon atoms of these inhibitors are tetrahedral when bound to the enzymes.

Binding, Competitive↗
PubMed1993

Mechanism of uptake of deglucoteicoplanin amide derivatives across outer membranes of Escherichia coli and Pseudomonas aeruginosa.

Teicoplanin is a glycopeptide antibiotic which is ineffective against gram-negative bacteria because of its inability to penetrate the outer membrane. Removal of the sugar residues and attachment of polyamines to carbon 63 yielded two dibasic deglucoteicoplanin amides, MDL 62,766 (766) and MDL 62,934 (934), with moderate MICs for Escherichia coli (2 to 4 micrograms/ml) and Pseudomonas aeruginosa (8 to 32 micrograms/ml) compared with those of the monobasic teicoplanin aglycone (16 and > 1,024 micrograms/ml, respectively). MICs were increased 16- to 32-fold by Mg2+ supplementation of Luria broth but not by Na+ supplementation at an equivalent ionic strength. Both 766 and 934 were capable of binding to P. aeruginosa lipopolysaccharide (LPS) at Mg(2+)-binding sites, as assessed by dansyl polymyxin displacement experiments. Furthermore, both compounds increased E. coli and P. aeruginosa outer membrane permeability to the hydrophobic fluorescent probe 1-N-phenylnaphthylamine (NPN), whereas the parent compounds teicoplanin aglycone and teicoplanin and the beta-lactam ceftazidime were totally ineffective. Addition of 1 mM Mg2+ blocked the increase in outer membrane permeability. Compound 766 had a lower MIC than 934 for both bacteria tested, bound to LPS with a higher affinity, and permeabilized outer membranes to NPN at lower concentrations. We propose that both deglucoteicoplanin amides exhibit increased gram-negative activity by virtue of their ability to access the self-promoted uptake pathway across the outer membrane.

Binding Sites↗
PubMed1984

Lipid A and resistance of Salmonella typhimurium to antimicrobial granule proteins of human neutrophil granulocytes.

Granule extracts from human polymorphonuclear leukocytes were prepared and fractionated by chromatography on Sephadex G75-SF. One fraction exhibited potent antimicrobial activity against an Rd1 lipopolysaccharide (LPS) mutant of Salmonella typhimurium. Susceptibility of the mutant to antimicrobial activity appeared to be due to binding of granule proteins to lipid A because isolated native LPS succeeded in blocking the antimicrobial activity of granule extracts whereas base-hydrolyzed LPS failed to do so. Centrifugation of control and base-hydrolyzed LPS-protein mixtures in cesium chloride gradients suggested that only control LPS formed complexes with antimicrobial proteins. Further evidence that bactericidal proteins from polymorphonuclear leukocyte granules interact with lipid A was that sublethal concentrations of polymyxin B (an antibiotic known to bind to lipid A) rendered target bacteria phenotypically resistant to granule proteins. Moreover, a mutant of S. typhimurium which synthesized a lipid A with decreased electronegativity due to increased 4-amino-4-deoxy-L-arabinosylation at the 4'-phosphate exhibited increased resistance to both polymyxin B and granule proteins. These results suggest that polymyxin B and antimicrobial proteins derived from polymorphonuclear leukocyte granules interact with lipid A in an analogous manner.

Antimicrobial Cationic Peptides↗